1. Field of the Invention
The present invention relates to polyaryl metal complexes, such as metallo macrocycles or Schiff's bases, intercalated into layered double hydroxides (LDHs) which are useful as stable catalysts, particularly for autoxidation of organic molecules. In particular, the present invention relates to cobalt phthalocyanine layered double hydroxides and cobalt porphyrin layered double hydroxides.
2. Prior Art
Metallo phthalocyanines and porphyrins are known to catalyze the selective autoxidation of certain organic molecules in homogenous solutions at relatively low temperatures. Iron derivatives, for instance, mimic much of the catalytic chemistry found for metabolic pathways involving P-450 heme proteins. This property is of interest for applications in remediation of contaminated ground water and industrial effluents. There is commercial interest in the application of the Co(II) phthalocyaninetetrasulfonate as thiol oxidation catalysts in petroleum fractions, for instance, but the practical utilization of the homogenous catalysts is, however, severely hindered by several problems. Firstly, the homogenous catalysts tend to deactivate quickly and this is thought to arise from the very nature of the materials in that the complexes tend to dimerize in solution. For example, the iron(II) porphyrins and phthalocyanines under oxidizing reaction conditions form dimeric forms containing LFe-O-FeL linkages (where L is a macrocyclic ligand) and in this form they are unable to bind and activate oxygen. Secondly, homogenous catalysts cannot be easily separated from the solution and the recovery costs are prohibitive.
The possibility of increasing the catalyst life and possible enhancement of the rate of the reaction lies in the ability to site isolate the catalyst on a support. Several supports have been reported to date, such as charcoal, polymers and zeolites. Site isolation in the zeolites has been achieved by the so-called "ship-in-a-bottle" synthetic methods. Typically this is done by in situ reaction of a smaller building block with a metallo form of the zeolite.
European Patent No. 0 453,021 A1 describes a process for preparing a ketone and/or alcohol by oxidizing a cyclic hydrocarbon with oxygen to form a hydroperoxide, followed by a decomposition of the hydroperoxide in the presence of a phthalocyanine or porphyrin metal complex immobilized on a carrier. The carrier as disclosed in this patent may be inorganic materials such as alumina, TiO.sub.2, SiO.sub.2 or organic carriers such as polystyrene, ethylenevinylacetate copolymer, acid anhydride-modified polyethylene. When a material such as silica is used as a carrier, halogenated porphyrins or phthalocyanines are heated over time in pyridine together with silica and then the excess porphyrines or phthalocyanines are washed off the silica.
The present invention discloses the use of certain planar or disc-shaped anionic metal complexes including macrocycles such as phthalocyanines, porphyrines and Schiff's bases. The metallo phthalocyanine contains at least four pyrrole rings and at least eight nitrogen atoms with four of them closer to the center containing a metal cation. Fused to the four pyrrole rings are four benzene rings and these rings can contain anionic substituents such as sulfonate, carboxylate and the like. The overall description is represented by the following formula: EQU Z.sub.n/a [M.sup.b+ PcTsc] (I)
where Pc represents the phthalocyanine or porphyrin or Schiff's base ring, Tsc represents four substituted anionic charge bearing substituents such as sulfonate or carboxylate distributed on all four rings or, alternatively, two substituents on two rings, Z represents the charge balancing cation such as sodium, n represents the overall anion charge on the phthalocyanine or porphyrin or Schiff's base, a is the charge of Z and M.sup.b+ is characterized in which the metal contained in the metallo macrocycle complex is a member selected from the group consisting of (a) a Group VII-B metal (e.g., Mn, Tc and Re), (b) metals from the cobalt and iron triads of Group VIII (e.g., Co, Fe, Rh, Ir, Ru and Os or (c) a mixture of at least two different metal macrocycles from (a) and (b). Examples of metallo phthalocyanines include Co (II) phthalocyaninetetrasulfonate, Co(II) phthalocyaninetetracarboxylate, Ni(II) phthalocyaninetetrasulfonate, Ni(II) phthalocyaninetetracarboxylate, Cu(II) phthalocyaninetetrasulfonate, Cu(II) phthalocyaninetetracarboxylate, Co(II)dinuclear dodecasulfonatephthalocyanine, Co(II)dinuclear dodecarboxyphthalocyanine, Cu(II)dinuclear dodecasulfonatephthalocyanine, Cu(II)dinuclear-dodecarboxyphthalocyanine, Ni(II)dinuclear-dodecasulfonatephthalocyanine, Ni(II)dinuclear dodecarboxyphthalocyanine. Examples of metallo porphyrines include Co(II)5,10,15,20-tetra (4-sulfonatophenyl)porphin, Co(II)5,10,15,20-tetra(4-carboxylatephenyl)porphin, Ni(II)5,10,15,20-tetra(4-sulfonatophenyl)porphin, Ni(II)5,10,15,20-tetra(4-carboxylatephenyl)porphin. Examples of metallo Schiff's base complexes include Co(II)bis-(salicylaldehyde)ethylenediaminebi-sulfonate, Co(II)bis(salicylaldehyde)ethylenediaminebi-carboxylate, Cu(II)bis(salicylaldehyde)ethylenediaminebi-sulfonate, Cu(II)bis(salicylaldehyde)ethylenediaminebi-carboxylate, Ni(II)bis(salicylaldehyde) ethylenediaminebi-sulfonate, Ni(II)bis(salicylaldehyde) ethylenediaminebi-carboxylate, Cu(II)pyrrole-bis(salicylaldehyde)ethylenediaminebi-sulfonate, Cu(II)pyrrole-bis(salicylaldehyde)ethylenediaminebi-carboxylate, Co(II)pyrrole-bis(salicylaldehyde)ethylenediaminebi-sulfonate, Co(II)pyrrole-bis(salicylaldehyde)ethylenediaminebi-carboxylate, Ni(II)pyrrole-bis(salicylaldehyde)ethylenediaminebi-sulfonate, Ni(II)pyrrole-bis(salicylaldehyde)ethylenediamine bi-carboxylate.
Under homogenous conditions these complexes are good oxidation catalysts for oxidizing a mercapto compound to a disulfide and as taught in U.S. Pat. No. 3,371,031 to Strong, a phthalocyanine or Schiff's base catalyst is usually preferred for the oxidation. These homogenous phthalocyanine and Schiff's base catalysts are also found to be effective catalysts for the oxidation of substituted phenols to their corresponding quinones. Vipin. M. Kothari and James J. Tazuma (J. Catal. 41, 180, 1976) have reported the autoxidation of 2,6-dialkyl substituted phenols using salcomines, the complexes derived from cobalt(II) and Schiff's bases of salicylaldehyde and ethylenediamine using N, N'-dimethylformamide as the solvent. Salcomines were found to catalyze the oxidation of monoalkylphenols and phenol but required higher temperature and more severe conditions compared to the Co(II)phthalocyanine. Deactivation of the homogenous catalyst is thought to arise from the dimerization of the complexes, particularly in the presence of hydroxide ions, and in this form, the complexes are unable to bind and activate molecular oxygen.
LDH's are a group of anionic clay minerals. These compounds have positively charged sheets of metal hydroxides, between which are located anions and some water molecules. Most common LDHs are based on double hydroxides of main group metals such as Mg and Al, and transition metals such as Ni, Co, Cr, Zn, and Fe. These anionic clays have a structure similar to brucite (Mg(OH).sub.2) in which the magnesium ions are octahedrally surrounded by hydroxyl groups with the resulting octahedra sharing edges to form infinite sheets. In the LDHs, some of the magnesium is isomorphously replaced by a trivalent ion such as Al.sup.3+. The Mg.sup.2+ Al.sup.3+ OH.sup.- layers are then positively charged, necessitating charge balancing by insertion of anions between the layers. One such anionic clay is hydrotalcite in which the carbonate ion is the interstitial anion, and has the idealized unit cell formula Mg.sub.6 Al.sub.2 (OH).sub.16 [CO.sub.3 ].4H.sub.2 O. However, the ratio of Mg/Al in hydrotalcite-like can vary between 1.7 and 5 and various other divalent and trivalent ions may be substituted for Mg and Al. In addition, the anion, which is carbonate in hydrotalcite, can be varied by synthetic means by a large number of simple anions such as NO.sub.3.sup.-, Cl.sup.-, OH, SO.sub.4.sup.2- ect. These LDH's, based on their structure, fall into the pyroaurite-sjogrenite group, where brucite-like layers carrying a net positive charge alternate with layers in which oxygen atoms of carbonate groups and water molecules are distributed on a single set of sites. Such LDH materials are described in U.S. Pat. Nos. 5,079,203, 5,114,691 and 5,114,898 to Pinnavaia et al.
A review article by W. T. Reichle in Solid State Ionics, 22, 135, (1986) summarizes some of the methods available for LDH synthesis. If a carbonate-containing product is desired, then the aqueous solution of magnesium and aluminum salts, i.e, nitrate, or chloride, is added to an aqueous solution of sodium carbonate with good mixing at room temperature. The resulting amorphous precipitate is then heated for several hours at 60.degree. to 200.degree. C. to obtain a crystalline material. Washing and drying completes the synthesis in quantitative yield. By employing this precipitation method, replacement of all or part of Mg.sup.2+ with other M.sup.2+ ions such as Zn.sup.2+, Cu.sup.2+ and the like, or replacement of Al.sup.3+ with other M.sup.3+ ions such as Fe.sup.3+, Cr.sup.3+ and the like is obtained.
Another important aspect of the synthesis of these materials is the ability to vary the nature of the interstitial anion. The preparation of hydrotalcite-like materials with anions other than carbonate in pure form requires special procedures, because LDH's incorporate carbonate in preference to other anions. Direct preparation of non-carbonate LDH's could be cumbersome requiring the exclusion of carbon dioxide at every step. Several alternative methods of intercalating non-carbonate organic and inorganic anions have been described in the prior art; for example, see Pinnavaia et al in U.S. Pat. No. 5,079,203, M. A. Drezdzon in Inorg. Chem., 27, 4628 (1988), K. Chibwe and W. Jones in Chem. Comm., 926 (1989). Hence, due to the availability of methods it is possible to obtain well defined non-carbonate intercalated LDH's. Park et al, Chem. Lett 2057 (1989) describes non-metalated tetrasulfonated porphyrin anion intercalated into the LDH structure. But it is well known by those skilled in the art that intercalating anionic metallo phthalocyanine or porphyrins could present unique problems. Although the rings bear anionic charge the positively charged metal cations could present difficulties since the host layers are positively charged and this could result in demetallation of the complex. It would be desirable to intercalate metallo macrocycles bearing an anionic charge on the rings into LDH hosts. Unlike polymers, which are organic, as supports for the metallo macrocycles for autoxidation reactions, anionic clay minerals are inorganic in nature and could function as long-lived practical regenerable supports.